In recent years, a display apparatus with a flat display as a display device is in widespread use for its ease of reduction in size and thickness. In many cases, such a flat display is used in a liquid crystal display apparatus that facilitates multicolor display. A transmissive liquid crystal display apparatus is generally provided with a backlight device to secure luminance on a display screen. Besides, a liquid crystal display apparatus using both reflective method and transmissive method, so-called transflective liquid crystal display apparatus is also provided with a backlight device as a light source for transmissive mode.
As the light source for backlight device, a fluorescent lamp, such as a cold-cathode tube, is commonly used. Examples of a major backlighting method include a direct lighting method where light emitted from a lamp enters a liquid crystal panel directly from the back of the liquid crystal panel, and a side lighting method where light emitted from a lamp, disposed on the side of a liquid crystal panel, is spread over the entire area of the liquid crystal panel through an optical waveguide.
For such a backlight device, an inverter controls illumination for luminance conditioning (dimming) of fluorescent lamps and other purposes. Particularly, a PWM inverter adjusts an electrical discharge time of a fluorescent lamp by controlling a pulse width of a pulse voltage applied at given intervals, which facilitates dimming, and the PWM inverter is therefore used for dimming control of fluorescent light for general lighting. The lighting control of a backlight lamp by PWM inverter is described in Patent Literature 1 and other documents.